Electric valve converting system



Sept. 6, 1938. .E, I 2,129,536

' ELECTRIC VALVE CONVERTING SYSTEM Filed Feb. 12, 1958 i'i l Inventor: Eugene H. Reid y i l i wh torney.

Patented Sept. 6, 1938 UNITED STATES PATENT OFFICE Eugene H. Reid, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York ApplicationFebruarylZ, 1938, Serial No.190,267

5 Claims.

My invention relates to electric valve converting systems, and more particularly to such systems providedwith means for suppressing reverse arcs within the valves of said apparatus.

It is commonly known that electric valve converting apparatus,.in operation, are subject to reverse arcs which may be occasioned by any of a number of disturbing operating conditions. If such reverse arcs within the valves are permitted to persist serious damagezmay becaused not only tothe valves themselves but to thesystem and other apparatus associated therewith. Hereto fore, there havebeen proposed certain arrangements which have had as their objects the elimination or suppression-of reverse arcs in electric valves.

One of such systems for controlling reversearcs or arc backs is disclosed in United States Letters Patent No. 2,088,436, granted. July 27,

1937, upon the application of Eugene..I-I..Reid

wrent to a safe value.

for improvements in a Vapor electric rectifying system. In ,this system the change in potential. between the cathodeand a conductive member in contact with theionizable vapor or gas .of the arelectric valve is used to control a means for aprespect to the cathodes, there is included .a current limiting resistor for this same purpose. Upon the occurrence of an are back and the application of a negative voltage to the grid it would be highly desirable if the grid" circuit did =not contain such current limiting resistors.

It is, therefore, an object of this invention to provide an improved electric valve converting system in which a negative potential will be impressed upon the anode shields or grids and yet have a relatively low resistance value in thegrid circuit,

It is anotherobject of this invention to provide an improved electric valve converting system in which the grid circuitunder normal operation will have a relatively high resistance value and under abnormal circuit conditions a rela-.

tively low resistance value.

In accordance with my invention, an electric valve converting apparatus is provided with conrductive anode shieldsor control grids upon which In the grid control type of. electric are impressed normally either continuous or periodic positive potentials to render the associated anode conductive. A substantially high negative potential is also connected to the shields or grids through suitable means such as a normally non-conductive electric valve. The control electrode of this-normally non-conductive electric valve is 50 connected to the system as to be responsive to transients due to the occurrence of reverse arcs or abnormal current conditions in the apparatus. For example, upon the occurrence of a reverse arc a conductive member in contact with the ionizable medium of the electric valve or in the instance of a metal container, this conductive container when provided with an insulated cathode changes its potential with re- I spect to the cathode, so that it becomes negative with respect to the cathode whereas under ordinary normal operating conditions it is positive with respect to its cathode. This reversal of polarity may be used to control the electrode of the normally non-conductive auxiliary electric valve. The normal current limiting resistors of the circuit for the shields or control grids are replaced by non-linear voltage-resistance elements which under normal conditions present a relatively high resistance value to the grid circuit, but which upon application of a high negative potential present to the circuit a relatively low resistance value.

For a better understanding of my invention, together with further and other objects thereof, reference is had to the following description taken in connection with the accompanying drawing in which the figure illustrates one embodiment of my invention in which a change in the potential of the conductive member in contact with the ionizable vapor of the valve with respect to its cathode is utilized to suppress the reverse are orare back in an electric valve.

Referring now to the single figure of the drawing, I have illustrated an electric valve converting system for transmitting energy from an alternating current supply circuit Hi to a direct current load device illustrated as the motor I I.

The system illustrated shows a transformer i2, an' electric valve l3, and a high speed direct cur-- rentcircuit breaker M, which may be of any of the several types well known in the art. The

, electric valve apparatus I 3, which may be any of the types Well known in the art, is shown as being a metal tank or other conductive container l5, an insulated mercury pool cathode It, a pair of anodes I1 and a pair of conducting shields or grids l8 surrounding the anodes H and insulated therefrom. While the arrangement illustrated shows a system for transferring energy from alternating current circuits to direct current circuits, it will be apparent that the invention is also applicable to inverting circuits and furthermore that any number of anodes may be utilized in the valve I3. It will also be apparent that a plurality of single anode valves may be utilized which may be provided with igniter electrodes and protective shields about the anodes. Similarly, the envelope may comprise a glass container and an auxiliary conductive member may be enclosed within the envelope so as to be in contact with the ionizable vapor within the valve. If the valve I3 is of the uncontrolled type, it is common to impress a positive potential upon the grid I8 in order to maintain, under normal conditions, the valve I3 in a conductive condition. One of the grid members I8 is shown as being connected through a circuit including a nonlinear voltage-resistance element I9, a positive potential source 20 and a resistor H to the container walls I5 or to a conductive member in contact with the ionizable vapor of the valve I3. The non-linear voltage-resistance element I9 may be of the type disclosed in United States Letters Patent No. 1,822,742, granted September 8, 1931 on the application of Karl B. McEachron. Such material has the characteristic of presenting under normal conditions a relatively high resistance value to the grid circuits and under abnormal conditions a relatively low value of resistance. A similar non-linear voltage-resistance element is connected in the circuit of the other grid member I8 and by way of illustration this is being shown as comprising a resistor 22 connected in parallel to a series circuit comprising a resistor 23 and a contact rectifier 24, which rectifier may be of the copper oxide type disclosed in United States Letters Patent No. 1,640,- 335, granted August 23, 1927 on the application of Lars O. Grondahl. Upon occurrence of abnormal current conditions the grids I8 are arranged to be connected through a suitable source of neg ative bias potential 25 and a normally non-conductive electric valve 26 to the conductive portions I5 of the electric valve I3. The normally non-conductive valve 26 is provided with an anode, a cathode and a control grid or electrode and may be any of the several types well known in the art, such as the grid glow or Thyraton type. The grid of the electric valve 26 is connected through a grid circuit resistor 2's to the cathode I6 of the electric valve I3.

The general principles of operation of the rectifying system. comprising the transformer I2, the electric valve I3 and the direct current load device II will be well understood by those skilled in the art, so that a detailed explanation is not deemed necessary. Under normal operating conditions, the grids I8 will be maintained at a posi-v tive potential with respect to the tank or conductive member I5 by means of the voltage supplied by the battery 26; and the tank member I5 is normally slightly positive with respect to the cathode I6. Under such conditions the apparatus I3 is completely conductive and the grids I8 permit the rectifying system to operate as an uncontrolled rectifying apparatus. It will be as sumed that the circuit breaker I4 is closed and that energy is being supplied to the direct current motor l I. Upon the occurrence of a reverse are or are back, a short circuit may appear across the transformer I2 or the current may rise to abnormally high values. Such abnormal current conditions will cause the circuit breaker I4 to open and thus interrupt the flow of reverse power but when the are back is occurring between the two anodes, the short circuit will not be removed from the transformer I2. Under abnormal conditions, however, the potential of the tank I5 reverses in polarity with respect to the cathode I6 substantially instantaneously so that the tank I5 or conductive member in contact with the ionizable vapor of the valve I3 is negative with respect to the cathode I6. If the cathode is not taken as a reference point on the apparatus but some other point such as ground or some conductor of which the absolute potential remains substantially constant under all conditions utilized, the change in potential between the tank or conductive member in contact with the vapor therein is utilized to actuate the grid of the valve 26. The necessary changes in the circuit of the control electrode or grid connections will be obvious to those skilled in the art. With the connections as described above, this results in placing a positive potential upon the control electrode of the valve 26 to render it conductive, thus connecting the grid I6 to the conductive member or tank I5 through the non-linear voltage-resistance element, the negative bias battery 25 and the electric valve 26. Upon the application of the high negative bias from the source 25 to the grid circuit the non-linear voltage-resistance element such as the element l9 and the combined elements 22, 23 and 24 now present to the grid circuits relatively low resistance values. Under this condition the are back will persist only for the remainder of the particular half cycle and thereafter the negative potential on the grids I8 prevents the discharge from continuing. If it is desired to prevent operation of the valve 26 upon occurrence of extremely short transients, a condenser may be connected between the grid and cathode of the valve 26 to absorb these short transients. In such cases it is preferable to provide the condenser with a grid leak in order to allow the charge to leak off the condenser.

It therefore will be apparent to those skilled in the art that the present invention may be applied to single and multi-anode tank rectifiers which may be either uncontrolled, grid controlled or controlled by starting or ignitor electrodes. In each instance it is desirable that under normal operating conditions the shields or grids should be connected in a circuit having a relatively high resistance value under normal operating conditions and a relatively low resistance value under abnormal current conditions.

While I have described what I at present consider preferred embodiments of my invention, it will be obvious to those skilled in the art that various changes. and modifications may be made in the circuit and instrumentalities without departing from my invention, and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. In combination with an electric valve comprising an envelope containing an ionizable medium, an anode, a cathode, a grid and a conductive member in contact with said ionizable medium, a circuit for said grid including a nonlinear voltage-resistance element having normally a high resistance value, and means cooperating with said conductive member upon abnormal conditions to apply through said non-linear element a negative bias potential to said grid.

2. In combination with an electric valve apparatus comprising an anode, a cathode, a grid and a conductive member in contact with the ionizable vapor of said apparatus, a circuit for said grid including a non-linear voltage-resistance element, and means responsive to a change of potential between said conductive member and said cathode for applying to said grid through said non-linear element a negative bias potential.

3. In combination with an electric-valve apparatus comprising a conductive container, an insulated cathode, a grid for said anode, a circuit for said grid including a non-linear voltageresistance element, and means responsive to a change in potential between said cathode and said container for impressing upon said grid 21. negative bias potential.

4. In combination with an electric valve comprising a cathode, an anode, a grid for said anode and a conductive member in contact with the ionizable vapor of said apparatus, a circuit for said grid including a non-linear voltage-resistance element normally presenting a high resistance value to said circuit, means responsive to a reversal of the potential between said cathode and said conductive member upon abnormal conditions for impressing a negative bias potential upon said grid circuit whereby said nonlinear voltage-resistance element presents a relatively low resistance value to said circuit.

5. In combination with an electric converter comprising a conductive container, an insulated cathode, a plurality of anodes and associated grids, a circuit for each of said grids including a non-linear voltage-resistance element normally presenting a high resistance value to said circuit, means for suppressing an are between said anodes comprising means responsive to a reversal of the potential between said cathode and said container for impressing a bias potential upon each of said grid circuits whereby said nonlinear elements of said circuits present low resistance value to said circuits.

EUGENE H. REID. 

